Year	Percent
1961	43.08531
1962	42.78963
1963	42.29035
1964	42.12918
1965	41.98013
1966	41.27484
1967	40.88342
1968	40.70892
1969	40.60955
1970	40.42414
1971	40.24358
1972	40.07635
1973	39.0475
1974	38.86694
1975	38.65124
1976	38.57853
1977	38.50703
1978	38.54581
1979	38.08652
1980	38.0635
1981	38.238
1982	38.0841
1983	36.66869
1984	36.75715
1985	36.80926
1986	36.67959
1987	36.69413
1988	36.94014
1989	36.96801
1990	36.64445
1991	36.80199
1992	36.51236
1993	36.3427
1994	36.28333
1995	36.12579
1996	36.03127
1997	35.92584
1998	35.86888
1999	35.81192
2000	35.63015
2001	35.3381
2002	35.16966
2003	34.96401
2004	34.74794
2005	34.61949
2006	34.45589
2007	34.29593
2008	34.04508
2009	33.87058
2010	33.67911
2011	33.41372
2012	33.1459
2013	32.91808
2014	32.89142
2015	32.94292
2016	32.35785
2017	32.16941
2018	32.14772
2019	32.12809
2020	31.53981
2021	31.47673